I have been fasting since a few months. After a few weeks I started noticing that in fasted state, I had this clenchy feeling in my jaws, kinda like the feeling you have with chattering teeth.

After another few weeks this feeling scattered throughout the rest of my body. A kind of clenching feeling resembling what you have when you have the chills/shivers, although I’m not really shivering. It’s also not really cramps.

It’s very annoying, but went away with eating or when turning the heat up.

Now, another few weeks later, the feeling doesn’t go away so easily anymore, not even with eating, and not when turning the heat up.

I don’t think I am experiencing quite the same thing as you describe, but I have noticed that now that it’s winter, I am feeling more uncomfortably chilled on fasting days — it’s just hard to warm up. I am not normally this way, in fact, I generally can’t wear a sweater to work because I get too hot running around the building. Maybe what you describe is a more extreme version of my experience of being chilly…?